The invention relates to a coupling sleeve for a hydraulic coupling. The coupling sleeve comprises receiving means to receive and arrest a coupling plug. The coupling plug includes a plug valve. The coupling sleeve further comprises a valve seat and a valve body. The valve body may be moved relative to the valve seat along a longitudinal axis into an open position or closed position. Towards the closed position, the valve body is loaded by a closing spring. A switching pin opens the plug valve. The switching pin passes through the valve body in the direction of the longitudinal axis. The switching pin leaves the body through a through-bore in the valve body in the direction of receiving member. The plug valve also includes a sleeve valve. A sleeve chamber is positioned between the sleeve valve and the valve seat of the valve body. A switching member is pivotably settable between two positions to establish a connection between a pressure agent connection at the sleeve end and the coupling plug. The switching member, with the coupling plug arrested in the receiving means, sets the valve body against the force of the closing spring. In order to switch the sleeve valve into the open position, the switching member is rotated to move the switching pin into the receiving member against the force of an opening spring to open the plug valve. The switching member, in an open position and with the coupling plug in the uncoupled position, enables automatic transfer to the valve body and sleeve valve into a closed position.
A coupling sleeve is described in DE 43 18 840 C2. Here, in case a coupling plug is unintentionally pulled out of the coupling sleeve with the valve body in the open position, or in case of unintentional actuation of the switching member, the coupling sleeve is transferred from the closed position into the open position, with the coupling plug in the uncoupled position, the oblong hole in the switching member provides a closed position for the valve body relative to the valve seat in the coupling sleeve. To close the sleeve valve and subsequently return the switching member into the closed position, it is difficult because the switching pin has to be moved against the prevailing system pressure in the sleeve chamber. This procedure is particularly complicated if, in the supply pipe in front of the sleeve valve, a blocking valve or a similar switching valve is present in a locked position. Thus, an enclosed volume exists which cannot be compressed. Under such pressure conditions, the pressure existing in the sleeve chamber cannot be reduced.
The unpublished DE 196 19 839 C1 reference describes a way to facilitate moving the valve body into an open position. Here, the shaft portion, which has one or several grooves on the outer face, is moved out of the valve body through the through-bore towards the receiving chamber to receive the coupling plug. The grooves extend parallel to the longitudinal axis. Also, the portion may include a stepped diameter. The grooves and stepped diameter ensure, provided the switching pin is in the correct position relative to the through-bore, that the pressure agent can escape from the sleeve chamber into the receiving chamber. According to a further solution described by the above reference, a metallic seal is provided in the form of a conical seat which comes to rest against a corresponding edge of the through-bore in the valve body when the coupling sleeve is in the closed position. However, if the switching pin is moved out of its closed position into the open position, pressure agent may escape from the sleeve chamber between the wall of the through-bore and the outer circumference of the sleeve chamber. This is also the case if the coupling sleeve is unintentionally opened when the coupling plug has been removed, with the switching pin in its forward position. Admittedly, the above-described measures facilitate the coupling operation, but the assembly is no longer leak-proof. This enables the pressure agent contained in the sleeve chamber to escape. Accordingly, since pressure agent quantities are in the region of several cubic centimeters, the escape constitutes an undesirable quantity.